The sorting of biological materials in the form of cells and microorganisms is typically carried out with a flow-cytometer, which has a sorting module.
A commonly known principle for the sorting of biological materials is brought about by first converting the liquid flow into drops, after which the drops are separated electrostatically.
With another principle, use is made of a method of separation where a volume element in a liquid flow is directed via a separate channel in relation to a main flow.
Examples of the latter principle are e.g. described in U.S. Pat. No. 3,827,555, where the separation is effected by means of mechanical valves, which are controlled on the basis of a signal from a photo-detector. However, the problem with the use of mechanical valves is that they have a relatively poor reaction time, and moreover that they unavoidably influence the flow pattern when they are activated.
In order to alleviate this problem, in U.S. Pat. No. 4,756,427 it is suggested that use be made of a piezo element which, however, is a relatively expensive component.
From WO 98/10267 a flow-switch is known where, by controlling of the part of a right and a left flow, an intermediate liquid flow can be positioned in such a manner that it can be directed through several branches at the outlets. This method is intended especially for the injection of a small liquid volume.